This invention relates to branched nitropolyphenylenes, branched polyphenylenes and mixtures thereof and to composites made therefrom.
Much effort has been expended on the synthesis and evaluation of polymers for high temperature use. The goal has been to extend the useful upper temperature limit at which polymers maintain their desirable properties to at least 300.degree.C and preferably to 500.degree.C or above. Among the polymers which have been evaluated for use in this high temperature range are polyphenylenes. These polymers are composed essentially of carbon and hydrogen in aromatic ring type structures, with the rings chemically linked to each other through the ortho, meta and para positions. Such polymers are to be clearly distinguished from other chemically similar phenylene type structures, such as polyphenylene oxide, polyphenylene sulfone and other polymers containing the designation "phenylene."
Polyphenylenes generally have been produced by techniques such as acid catalyzed oxidative coupling of the benzene ring in various aromatic compounds. The polyphenylenes produced by these processes possess some degree of high temperature thermal stability, but they are generally linear (para-polyphenylene) polymers which are relatively insoluble and infusible. Polyphenylenes have been produced which do possess certain limited solubility, but these have generally been at number average molecular weights of only about 1,000 to 2,000. Generally, these low molecular weight polyphenylenes contain only a low degree of branching, that is, they are still relatively linear polymers which contain long linear segments.
Recently, Wennerberg and Wang in U.S. Pat. No. 3,792,099, incorporated by reference herein, disclosed novel branched polyphenylenes which possessed increased solubility and excellent thermal stability over a number average molecular weight range from about 1,000 to over 10,000. These highly branched polyphenylene resins can be produced by the process described in U.S. Pat. Nos. 3,855,332, 3,829,518 and 3,798,281, all incorporated by reference herein. Branched polyphenylenes of this type can be used in a number of high temperature resistant composite applications. However, these unmodified branched polyphenylenes cannot directly be used to make composites with glass, carbon or graphite fibers. Attempts to mold composites of this kind end in failure, usually due to delamination of the structure caused by insufficient bonding or interaction between the polyphenylene resin and the fiber.
It has now been discovered that, when the branched polyphenylene resin is mixed with the branched nitropolyphenylene resin described herein, composites having good structural integrity and strength can be obtained with glass, carbon and graphite fibers. It has also been discovered that a polyphenylene resin mixture containing both a branched nitropolyphenylene resin and a branched polyphenylene resin produces asbestos fiber composites having better mechanical strength after thermal aging than asbestos composites prepared with relatively low molecular weight branched polyphenylene alone.